The present invention relates to a LED lens and a LED assembly thereof, especially to a Plano-Fresnel LED lens whose peak intensity is an elliptic distribution pattern in a LED assembly, being applied to LED lighting devices, flashlights of mobile phones or cameras.
LED with features of low voltage, low power consumption and long operation life has been broadly applied to indicators, illuminators and so on. Moreover, due to pure light color, compact volume and flat package, LED is also used on flashlight of mobile phones. Yet light emitted from LED chip is a point source with uneven brightness. Thus a lot of studies focus on light collection. Besides minimization of chip size, improvement of light emitting efficiency, the lens used is also an important direction of technical development.
Along with development of modern technology, electronics are getting more miniature, compact and multi-functional. A lot of electronic products such as digital still cameras, PC cameras, network cameras, mobile phones and even personal digital assistant (PDA) are equipped with a lens. The LED lights or flashlight applied to such products are formed by a single or multiple LED array(s). For convenience of easy carrying and humanized design, LED flashlights or lighting devices not only meet requirements of luminous flux such as combinations of LED elements with different distribution patterns but also require miniature and lower cost.
In lens design of LED, there are two types-primary optical lens and secondary optical lens. The primary optical lens is a lens directly packaged on the LED chip and is for concentrating light while the secondary optical lens is an LED array formed by signal chip or a plurality of LED chips for spreading light beams. The conventional design of the primary optical lens is shown in ES2157829, symmetrical aspherical lens is used. Refer to JP3032069, JP2002-111068, JP2005-203499, US2006/187653, and CN101013193, spherical lens is used as primary optical lens.
In JP2002-221658, spherical lens is applied to Bulk-type LED. In high-level applications, the primary optical lens not only concentrates light but also generates specific distribution pattern with even peak intensity such as large angle, small angle, round or elliptic distribution pattern. The primary optical lens is used in combination with the LED array so as to achieve optimal optical effects.
The application of the primary optical lens is shown in FIG. 1A & FIG. 1B. A lens 23 is covered over a LED chip 21. Light emitted from the LED chip 21 passes through the lens 23 to be concentrated to form a preset light pattern. Or a layer of secondary optical lens is added over the primary optical lens for brightness uniformity. There are various designs of the primary optical lens and some of them use a Fresnel optical surface, as revealed in WO/2003/083943, JP2005-049367, U.S. Pat. No. 6,726,859, US2007/0275344, US2008/0158854, EP1091167, and TW200711186 etc.
However, above conventional technique uses Fresnel lens covered over a plurality of LEDs, working as a secondary optical lens like a projector. Due to fast development of LED light emitting efficiency, the applications of a single LED have become more important. In the LED array or light sources formed by a plurality of LEDs, the brightness become in uniformity due to compensation of cross light beams through the lens. As to the single LED, the design of the primary optical lens is more complicated than that of the LED array or light sources formed by multiple LEDs because both the light concentration efficiency and the uniformity of brightness of the primary optical lens should be considered. A set of Fresnel zone plates is disposed on surface of the Fresnel lens and a zone pitch thereof is increasing gradually from the inside to the outside or from the outside to the inside. Besides light guiding and light collection, the Fresnel lens with features of light weight, compact volume and plastic nature and lower cost is suitable for being applied to lighting systems. For example, in JP2005-257953 and US 2006/0027828, a Fresnel lens with a single-side or double-side is disposed over a LED light source so as to generate uniform brightness, as shown in FIG. 1A & FIG. 1B. Refer to TW560085, by a paraboloid surface and a Fresnel lens, reducing the divergent light and uniform brightness may be formed. Furthermore, refer to Korean 1020070096368 and TW 1261654, a LED primary lens is made by a Fresnel lens but the distribution pattern thereof is a round distribution pattern.
However, as to multiple point LED lighting systems, brightness uniformity of both illuminance and light intensity should be considered. Conventional techniques usually use a certain ratio of the zone pitch to the zone height or changing zone pitch with changing zone height. For lighting system formed by a plurality of LEDs, changing zone pitch is better for matching requirements of uniform illuminance/light intensity. As to a single LED primary optical lens, the zone pitch depends on optical properties of the lens. Although the Fresnel lens with complicated surface and higher manufacturing cost, it provides better light efficiency and brightness uniformity, especially being applied to lighting devices with a single LED. In order to make light from single LED achieve higher efficiency, the present invention provide a primary optical lens of the LED made by Fresnel lens so as to concentrate light from surface of the LED chip and generate an elliptic distribution pattern with uniform peak intensity.